In software like ETABS, you can add or subtract while moving or adding a new beam, but as of now, STAAD does not have this facility. To do this, the user needs a calculator for such tasks. If STAAD had this feature, it would save time and effort and make STAAD more user-friendly.
Thank you for posting this idea. Can you suggest examples of the calculations you are thinking of? Currently you can move selected objects by a specific amount or by measuring between two points (nodes) in the model and STAAD will do the calculation for you. What other calculation are you thinging of?